Traversing tree in Python

[Daniel]

Hi,

I'm using Antlr with Python3. I've following code so far:

def main(argv):

    input = FileStream(argv[1])

    lexer = ConnectivesLexer(input)

    stream = CommonTokenStream(lexer)

    parser = ConnectivesParser(stream)

    tree = parser.prog()

Could you point me the way how to traverse the tree to evaluate something? Maybe is there some tutorial or documentation?

Thanks.

[Jonathan Coveney]

I'm not sure what you mean? generally the way it works is that your parser does the work necessary to either generate a data structure for further processing, or it does the evaluation itself. basically parser.prog() should be doing the work.

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[Terence Parr]

I think you want to use a listener or visitor generated by antlr tool :)

Ter

[Daniel]

Yes, I know that I should use listener or visitor generated by antlr tool.

I want to use visitor pattern, but I don't know how to use it exactly.

I asked for pointing a way (or maybe some tutorial) how to use visitor pattern in Python.

To learn the tool I've very simple grammar now:

grammar Gram;

prog: (expr NEWLINE)* ;

expr: left=expr op=('*'|'/') right=expr

    | left=expr ('+'|'-') right=expr

    | atom=INT

    | '(' expr ')'

    ;

NEWLINE : [\r\n]+ ;

INT     : [0-9]+ ;

And the visitor generated looks like:

class GramVisitor(ParseTreeVisitor):

    def visitProg(self, ctx):

        return self.visitChildren(ctx)

    def visitExpr(self, ctx):

        return self.visitChildren(ctx)

Could you explain me what should I do further on this simple example?